The present invention relates to a method and apparatus for attachment of a conductor to a cermet heating element.
In combustion systems used for combusting a specimen for subsequent analysis of the type disclosed in copending U.S. patent application entitled COMBUSTION SYSTEM, filed on Nov. 9, 1978, Ser. No. 958,967, and assigned to the present assignee, cermet heating elements are employed in the resistance heating furnace. One type of resistance heating element is made of molybdenum disilicide and is commercially available and sold under the trademark KANTHAL.RTM.. These elements provide the relatively high temperatures necessary and desirable in combustion systems for specimen combustion for subsequent analysis.
The KANTHAL.RTM. heating elements typically are provided from the manufacturer with ends for receiving clamp-on connectors. The ends are aluminum coated to provide an electrical connection to the heating elements with a standard clamp-type connector. It has been found that such connections, although initially operating satsifactorily, have a marked tendency to oxidize due in part to the exposure to high temperatures in the furnace environment resulting in arcing at the junction of the conductors which supply the operating current and the heating element. The oxidizing naturally results in reduction in the current supplied to the heating element and further breakdown of the connection and prevents the furnace from reaching its desired operating temperature. It is necessary, therefore, to frequently replace the heating elements which takes time and shuts the furnace down during replacement. In addition, the molybdenum disilicide is extremely brittle and elements can easily be broken during the replacement process.
The prior art has suggested a mechanical press-fit connector for attaching a conductor to the heating element. It has been found that such a mechanical connection alone does not operate successfully and suffers from some of the same problems as the clamp-on connectors normally employed. Thus, there exists a need for a connecting system for providing a permanent mechanical and electrical connection of a conductor for supplying current to such heating elements which avoids the problems in the prior art structure.